parallax mapping bugs

[illwieckz]

I noticed yesterday that XreaL had working parallax mapping, I know Darkplaces (used by Xonotic) has it too. What's missing to have that effect in our maps?

• ship height maps
• automatically discover height map in normal map alpha channel
• fix the reversed height map bug
• support parallax offset

[DolceTriade]

We had (have?) it too. But it was SUPER expensive and no one could use it. In order to use it, we'd need to generate an additional height map for each of our normal maps I think...

[mjstahlberg]

I recall there is a texture shader keyword that needs to be set in order for the effect to appear. Not sure if height maps needed to be included.

[illwieckz]

So, after investigation, I discovered that Dæmon engine…

• requires height maps (there is no magic computation of height map from normal map at run time)
• expects height maps to be stored in alpha channel of normal maps
• requires a special keyword to be set in shader before the normalMap stage, this keyword is named parallax and would have been best named heightMapInNormalMap
• does not know how to load height map that is not stored in a normal map alpha channel

So, to get parallax in game we need a lot of work to do, but that's possible.

I discovered that 2010 edition of XreaL shipped height maps for ex texture set (as external files) and trak5 one (in normal map alpha channels), but better than that, I discovered that xonotic ships height map for almost every texture they ship, including pk01, pk02, trak5, ex… 99.99% of their height maps are stored in normal map alpha channel, without requiring shader keywords. Some rare files (less than 10 in their xonotic-maps pk3) are stored as external files.

But another great news, they have code (GPLv2+) to generate height maps from normal maps, in three stages:

• makenorms.sh
• fft-normalmap-to-heightmap-soft.sh
• fft-normalmap-to-heightmap.c

So, what we can do:

• import their height maps
• compute the others

What could be good:

• not requiring any shader keyword to guess the availability of an height map in a normal map file
• optional heightmap loading from dedicated file, perhaps by merging the height map to normal map alpha channel in engine so the internal representation is kept

So, it requires a lot of work, but we can do it for Unvanquished.

[illwieckz]

Quote from #159:

Note that since Xonotic ships a heightmap with almost all its normalmap, I enabled temporarily parallax on all shaders just to have a look. It works (and I haven't experienced preformance issue) but I discovered that xonotic heightmaps are upside down, or our engine is.

Perhaps it's a trick to not have to detect the presence of heightmap hidden in alpha channel of normalmap, as a missing alphachannel would mean a flat surface at the good level. Currently our engine displays a flat surface at the wrong level if we enable parallax on a normalmap without heightmap in alpha channel.

Since we never shipped heightmap file, we are at a redemption time allowing us to change the heightmap orientation in engine if it's more clever to do this way.

[illwieckz]

If I understand things well, according to the way a height map is stored, in one case black is up and in the other case black is down. In Dæmon the lack of alpha channel in normal map (storing the height map) produces a down height map, if heightmap was expected upside down, I guess a missing alpha channel in normal map would produce a up height map. What do people think about it? 🤔

@gimhael @cmf028 @Amanieu @Kangz any knowledge to share ? 😃

[illwieckz]

Setting r_parallaxDepthScale -0.03 displays parallax correctly, as an additional proof xonotic's height maps are reversed (or Dæmon engine is):

It proves that parallax works in engine if height maps are correctly provided, I see no performance issue.

[illwieckz]

more sreenshots: